Patients with systemic lupus erythematosus (SLE) have autoantibodies to T cells; in this study we looked, in particular, for antibodies to the interleukin-2 (IL-2)-receptor on T cells. Four out of ten sera from patients with SLE blocked the IL-2 induced proliferation of PHA blasts or IL-2 dependent T cells. However, no inhibition by SLE sera of binding of radiolabeled IL-2 monoclonal anti-IL-2 receptor antibody of 125I- to these cells was observed. In a related study we examined whether B cells from patients with SLE were normally activated to proliferate in response to anti IgM. B cells from patients with SLE either responded poorly to such a stimulus or responded in a super-normal fashion. These responses were not correlated with the clinical state of the patient. In other experiments PHA supernatants containing stimulating lymphokines were added to the system. This had no effect on the response of the B cells from SLE patients that had been previously unresponsive.